The present invention relates generally to inductive reader devices for use with contactless smartcards, radio frequency identification devices and other transponders, and in particular to an inductive reader device with an integrated antenna and signal coupler.
Inductive reader devices are known for use with transponders, such as contactless smartcards and radio frequency identification devices. In radio frequency communication systems employing readers and transponders, the reader typically provides a radio frequency excitation signal. When a transponder is brought in close proximity to the reader device, electromagnetic coupling via the excitation signal powers the transponder and enables the transponder to generate a radio frequency response signal. This response signal is electromagnetically coupled to the reader. A data signal from the transponder included in the response signal is received by the reader and used for processing.
FIG. 1 is a block diagram showing schematically a known inductive reader device 10. Reader device 10 includes a transmitter 12, a receiver 14 an antenna 16 and a transformer 18. Transmitter 12 generates a radio frequency excitation signal using a signal source 20, which is typically controlled by a control circuit and a modulator that modulate commands onto the excitation signal. Transmitter 12 is directly connected to antenna 16. Antenna 16 is a coil having a predetermined inductance. Antenna 16 is typically implemented as a coil etched on a printed circuit board. Antenna 16 is generally made to consume as large an area as available in order to improve electromagnetic coupling between the reader device 10 and a transponder. Antenna 16 is directly connected to transformer 18. Transformer 18 is a discrete component that is separate and apart from antenna 16. Transformer 18 is connected to receiver 14. Transformer 18 does not inductively couple to a transponder. Transformer 18 is used to electrically receive from antenna 16 a data component of the modulated response signal returned by a transponder. This signal is then received by the receiver 14, which is directly connected to the transformer 18. The received signal is used by the reader circuit in accordance with the application, for example, security identification, smartcard transactions, etc.
One problem with the reader device 10 shown in FIG. 1 is the use of the discrete transformer 18. Transformer 18 is physically large and consumes valuable printed circuit board area. Transformer 18 is relatively expensive as well. In addition, some discrete transformer components are prone to failure, impacting the reliability of the product. Also, the characteristics of the transformer are required to be matched to the antenna, which may require custom transformer components for some reader devices.
FIG. 2 shows a known reader device 50 that eliminates the need for a discrete transformer, such as transformer 18. Reader device 50 includes a transmitter 52, a receiver 54, a transmitter antenna 56 and a receiver antenna 58. Transmitter 52 generates an excitation signal that is emitted by transmitter antenna 56. Transmitter antenna 56 is a coil. Electromagnetic coupling is used to transmit the excitation signal to a transponder brought in close proximity to transmitter antenna 56. Rather than receiving the responsive signal from a transponder via the same antenna element, as is the case in reader device 10, the receiver antenna 58 is provided for coupling to the transponder to receive the responsive radio frequency signal. Receiver antenna 58 is directly connected to receiver 54 to transfer the received responsive signal to the receiver. As illustrated in FIG. 2, transmitter antenna 56 and receiver antenna 58 share an available antenna area 60. The antennas 56, 58 are implemented as traces in a printed circuit board. The antennas are electrically isolated. The antennas partially overlap each other for mutual flux cancellation, which is required to isolate the transmitter and the receiver for proper circuit operation. Since the antennas must overlap partially, the total antenna area cannot be used for any one antenna. Therefore the size of both antennas is compromised in comparison to the total available antenna area. The reduced antenna area reduces the operating range of the reader device. This may be undesirable, in particular, for small portable reader devices.
Therefore, a need exists for a cost effective reader device with minimal limitations on operating range due to antenna size.